Without limiting the scope of the invention, its background is described in connection with emulator test systems used to model signal response over communication channels.
Advanced forward link trilateration (AFLT) is a handset-based geolocation technology that has been standardized for the emergency location of CDMA terminals by the Telecommunications Industry Association's TR-45.5 in IS-801. In order to provide the appropriate measurements for AFLT-based positioning, the mobile device must measure the time differences between CDMA pilot signals, where the term CDMA pilot signals specifically refers to the serving cell pilot signal and neighboring cell pilot signals. The observations from two such neighboring cells along with the serving base station’ coordinates are minimally sufficient to determine the location of the mobile device (although, in practice, more pilot signals may be captured in order to reduce the final location error). In the AFLT implementation, the terminal uses IS-801 standardized messaging to convey the measurement data to the PDE (Position Determination Element) by way of the CDMA network. Finally, at the PDE, the measured time (phase) differences can be converted to range differences that can be used to formulate a simultaneous system of nonlinear equations. In the absence of any measurement or systematic error, the intersection of these equations unambiguously defines the handset's location.
The FCC has defined a set of accuracy requirements for E-911 calls, which are collectively known in the industry as the E-911 Phase II mandate. The mandate states that handset-based solutions should locate the E-911 caller to within 50 meters for 67% of the calls and to within 150 meters for 95% of the calls. The new ALI (Automatic Location Identification)-capable handsets must fulfill the FCC's E911 Phase II location accuracy requirement by October 2003.
FCC OET Bulletin No. 71 defines a statistical approach for demonstrating compliance for empirical testing. If n denotes the number of measurements, the rth and sth measurements are denoted as xr and ys, respectively. x and y are the percentile points associated with probabilities p1 and p2 respectively, then the probability that x is less than xr while simultaneously y is less than ys is given by the formula:
      confidence    ⁡          (                                                                  x                ≤                                  x                  r                                            ,                                                y                  ≤                                      y                    s                                                  ;                                                                                        n              ,              r              ,              s              ,                              p                1                            ,                              p                2                                                        )        =                                          ∑                          i              =              1                                      r              -              1                                ⁢                                          ⁢                                    ∑                              j                =                1                                            s                -                1                                      ⁢                                                  ⁢                                          (                                                                            n                                                                                                  i                                                                      )                            ⁢                              (                                                                                                    n                        -                        i                                                                                                                                                n                        -                        j                                                                                            )                                                                                                                            p                1                i                            ⁡                              (                                                      p                    2                                    -                                      p                    1                                                  )                                                    j              -              i                                ⁢                                    (                              1                -                                  p                  2                                            )                                      n              -              j                                          p1=0.67 and p2=0.95. This formula is used in order to verify compliance.
This mandate has a tremendous impact on the carriers as well as the vendors, so it is rather important to establish reproducible and non-discriminatory test scenarios, testing methods and procedures in order to verify that the mobile phones fulfill these and possibly other accuracy requirements. As is the case with mobile phone compliance and verification testing, the carriers/vendors also need a standardized test environment in which location system calibration and verification can be performed. Therefore, a standardized laboratory test system, which can be used in lieu of extensive field-testing, can be used as a basis to verify the location accuracy for different brands of the phones in different (emulated) environments—and this type of system is currently in great demand. In addition, laboratory testing may also reduce the number and cost of field trials.
Prior to widescale deployment of AFLT, handset manufacturers and infrastructure vendors require a standardized, well-defined and repeatable method for testing system-integrated performance in a real-time re-configurable test system. This intermediate stage of testing may, in fact, circumvent the need to schedule field tests at all but a nominal number of live test sites prior to implementation. At least two of the major test equipment vendors have already developed E911 Phase II compliance verification system that could be used for testing the A-FLT location technology. The current approach is to use state-of-the-art CDMA network emulation hardware with programmable impairments in order to model some of the real-world cellular network phenomena that degrade system performance. They also use purely stochastic radio channel modeling that is either based on channel models that are obtained directly from the literature or from those published by the standards bodies for the compliance testing of mobile devices. While these models may capture some of the important aspects of the radio channel for different multipath environment (such as urban, rural and suburban), they cannot closely model the channel impulse response that will be encountered in a particular location. Thus, although a rural channel model may give some indication of the average channel properties for an area that falls into this classification, one might find that the actual deviations of the true radio channel from the stochastic channel model in a particular rural area might indeed be significant. Hence, it is readily apparent that the E911 Phase II compliance and verification systems that have been designed are not customized to predict the location accuracy for specific geographical areas.
Next generation of hardware-in-the-loop test apparatus and systems should provide a mechanism for emulating, with as much detail as is feasible, some of the market-specific conditions that will differentiate the performance in one network/environment/locale versus another. As systems evolve towards use of smaller cell sizes and increasingly there is need to deploy smarter networks, there is an accompanying need to provide a more realistic model of impact of the landscape/terrain/manmade features on the characteristics of the received radio signal. This requires the use of more sophisticated channel prediction techniques that are capable of providing market-specific channel data that is a better representation of the channel measurements that would actually be obtained during extensive field-testing.
As may be seen, an improved emulating system for determining positional coordinates for a selected geographic area model could provide significant advantages over existing systems.
What is needed, therefore, is an improved manner by which to test a mobile terminal for its compliance in E-911 Phase II accuracy requirements.
It is in light of this background information related to testing of operation of mobile terminals that the significant improvements of the present invention have evolved.